As daunting as securing your Linux system might seem, every extra step makes a difference. It’s almost always better to make a modest stride than let uncertainty keep you from starting. Fortunately, there are a few basic techniques that greatly benefit users at all levels, and knowing how to securely wipe your hard drive in Linux is one of them. Because I adopted Linux primarily with security in mind, this is one of the first things I learned. Once you have absorbed this lesson, you will be able to part with your hard drives safely.
From: Linux Insider